The leading campaigners came together for the Telegraph/Huffington Post Debate at the London headquarters of YouTube, facing questions from an audience of readers, journalists and YouTube stars.

After 90 minutes of heated exchanges, our columnists highlight the key moments in the debate, and explain what they tell us about the result of next week's referendum.

Juliet Samuel - the positive sides of a row about immigration

Boris Johnson struck a positive tone on immigration by emphasising that he is the descendent of migrants. He was preempting Alex Salmond who launched a passionate defence of immigrants: "I am fed up of seeing them presented as a negative. It's not fair it's not right and it's not true," he declared to applause.

His aim was to paint the Brexiteers as the nasty ones. But it backfired when Tony Smith, the man in the audience asking about immigration declared he wasn't anti-immigration but just wanted to know how public services could cope practically with the influx.

Mr Johnson was almost skewered by Mr Salmond when he admitted that he hadn't read the Bank of England study he was quoting. It states that there is a small fall in wages when immigration rises. "I want to nail this," said Mr Salmond. But he didn't. The point he seemed keen to make is that the wage effect is extremely small. But Boris won back the initiative by declaring that Salmond had confirmed what he was saying.

Tim Stanley - a glimpse of what might have been for Labour

Liz Kendall's answers were reasoned and passionate and -- this is important -- she wasn't afraid to deploy blue language. She came across like a well-informed ordinary citizen. "If you don't believe the politicians," she said at one point, "and I don't blame you if you don't..."

In fact she was so good that it raises two tantalising "what ifs?". What if she'd been elected Labour leader? Given the Government's current troubles, have no doubt Labour would be leading in the polls. What if Labour was leading the Remain campaign with her enthusiasm? They'd be making a progressive, positive case for the EU rather than David Cameron's negative, fearful one.

There was a powerful moment when Ms Kendall said that, yes, immigration puts a stretch on services but that "you're more likely in the NHS to be helped by a migrant than be in a queue behind them." People like her really believe in the EU - and they should have been leading the argument for it.

James Kirkup - self-control shows Boris is serious about the top job

Personal attacks on Boris Johnson have been one of the defining features of the referendum. Inevitably Alex Salmond couldn’t resist the temptation, suggesting that Mr Johnson’s Leave campaign is really about his ambition to become prime minister. A similar barb came from the audience later: “You’re in it for yourself.”

The attacks fell flat. That’s largely (and sadly) because most voters have a fairly low opinion of politicians: they assume they’re all self-interested careerists, so accusing any one politician of being a self-interested careerist is unlikely to do much damage.

More important still was Mr Johnson’s response: he didn’t respond. Instead of playing the joker, answering with a quip (he once said he was more likely to be reincarnated as an olive than become PM) he stayed silent, refusing to engage. That’s the self-discipline he’ll need if he’s going to persuade people he’s the sort of serious figure who can be prime minister.